Field of the Invention
The present invention relates to a plastic blow molding device, and more particularly to a plastic blow molding device for forming threadless blank.
Description of the Prior Art
Plastic bottles or cups can be formed by applying blow molding techniques to a blank 6 in a bottle mold 5. In detail, as shown in FIG. 6, the bottle mold 5 defines a forming space 51 therein for disposing the blank 6 and for applying blow molding to the blank 6. A bottom molding-base 52 is assembled to one of two opposite ends of the bottle mold 5, while a gas blowing portion 52 is assembled to the other end of the bottle mold 5. In addition, a thread section 61 and an annular protruded portion 62 are defined at one end of the blank 6 corresponding to the gas blowing portion 52, such that the blank 6 can be positioned via the thread section 61 and the annular protruded portion 62 when the blank 6 is molding. In practice of the blow molding technique, the bottle mold 5 is pressed downward to position with the annular protruded portion 62 of the blank 6, so that the blank 6 can sustain the pressure generated by gas blowing from the gas blowing portion 52, thereby changing the shape of the blank 6.
Cups of bottles made by the aforementioned technique have thread section 61 and annular protruded portion 62 at one end thereof. However, the thread section 61 and the annular protruded portion 62 are not necessary for some products, and the thread section 61 and the annular protruded portion 62 have to be cut from the products. Those materials cut from the product become waste and cannot be reused. In addition, after those unnecessary materials are cut from the products, sharp edges or corners may be formed on the products, thus the products have to undergo an additional polishing and milling process to smooth the surface. Consequently, the manufacturing of the conventional is complicated.
The present invention is, therefore, arisen to obviate or at least mitigate the above mentioned disadvantages.